This invention relates to the tensioning of drive belts and deals more particularly with a device that serves to adjust the tension of a drive belt such as the alternator belt of an automotive engine.
Various accessories such as alternators, compressors, pumps and the like are commonly driven by the engine of an automobile, truck or tractor, or by an industrial engine. Typically, the accessory is driven by a pulley which is in turn driven by an engine driven pulley through a drive belt. The accessory is usually mounted on the engine in a manner permitting it to be adjusted in order to tighten the drive belt. To adjust the belt tension, a bolt which extends through a slotted plate and is threaded into the accessory must be loosened, and a pry bar is normally used to pry the accessory until the belt is properly tensioned. Then, the bolt is tightened again.
As can easily be appreciated, this procedure is rather difficult to carry out by persons lacking in mechanical skill, and it requires the expenditure of considerable physical effort. Also, there is often inadequate space available for the pry bar to be properly applied. Even if there is sufficient room to use the pry bar, the possibility always exists that it will damage the alternator or other accessory, the electrical wiring, heater hoses, air conditioner hoses, fuel lines, or other components of the engine. As a result, many belts are not maintained at the proper tension, and the operating lives of the belt and pulleys are reduced due to the belt slack.
Although there have been attempts made to simplify the tightening of drive belts, the results have not been entirely satisfactory. Arrangements of the type shown in U.S. Pat. Nos. 2,494,360 and 2,643,551 to Russell and 2,341,992 to Jarrett require sliding carriages that take up considerable space which is often at a premium in engine compartments. Also, the need for cranks and other complicated mechanisms makes these devices too costly and complex to be practical. Lever operated devices such as those shown in the Stoddy U.S. Pat. No. 1,799,261 and Ensinger U.S. Pat. No. 2,458,575 patents are likewise characterized by excessive complexity and by mechanical problems resulting from by the need for cams, latches and similar components. Cost and complexity problems are also encountered by arrangements that require special castings or other specially constructed motor mounting devices, such as shown in U.S. Pat. No. 2,020,764 to Bradford and U.S. Pat. No. 4,240,368 to Adams.
The approach taken by Ireland et al in U.S. Pat. No. 1,413,028 is somewhat less complicated, although it does require a hinged structure for mounting the accessory and is less than satisfactory in this regard. The mechanism disclosed in U.S. Pat. No. 3,922,927 to Shiki et al must be factory or shop installed because its various parts must be welded or otherwise permanently attached to the accessory and its adjustment plate. Accordingly, this device is not suitable for field installation and requires considerable mechanical skill to install in any event.
The present invention is directed to an improved belt tensioning device which is simple and economical to construct and easily installed without the need for special tools or mechanical ability. In accordance with the invention, two angle brackets are added to a slotted plate on which an alternator or other engine accessory is mounted for angular movement to adjust the tension of the belt which drives the accessory. One bracket is directly connected to the plate by a bolt. The other bracket receives another bolt which fits through an arcuate slot in the plate and is threaded into the accessory. This bolt thus serves both to connect the second angle bracket to the accessory and to lock the accessory in place once the belt tension has been properly adjusted.
A machine screw extends between the two angle brackets and is threaded through one of them. The screw extends loosely through an opening in the other bracket and is restricted against axial movement by the screw head on one side and by a nut secured to the screw shank on the other side. When the bolt which extends through the arcuate slot is loosened, the machine screw can be turned and acts as a screw drive mechanism to move the angle brackets farther apart, thus tightening the belt which transmits power to the accessory. Once the proper belt tension is achieved, the bolt is tightened again to secure the accessory in place.
It is a particular feature of the invention that the proper belt tension can be achieved and maintained in a precise manner without the need for a pry bar or any special tools and without the need for mechanical skills or physical strength. The only tool required is the same wrench that is required in any event to loosen the adjustment bolt. The screw drive provides mechanical advantage which minimizes the physical effort that is necessary to tighten the belt. Equally significant is the fact that all of the components simply bolt onto existing parts of the engine. Consequently, the device can be installed in the field and need not be factory or shop installed by specially skilled mechanics.